In recent years, in the field of electronic materials, semiconductor devices have been made increasingly higher in degree of integration, faster in operating speeds, and higher in performance. Along with this, signal delay, considered to be caused by greater interconnect resistance of the semiconductor integrated circuits or greater electrical capacity between interconnects, has become a big problem. In order to solve the problem of the signal delay and to increase the operating speed of semiconductor devices, it is necessary to use a low permittivity material for the insulating film in multi-layer interconnect structures.
In order to decrease the permittivity of an insulating film, techniques such as decreasing the polarity of the material and lowering the density of the insulating film have mainly been studied. For example, as disclosed in Japanese Unexamined Patent Publication No. 2006-265513, in order to decrease the polarity, it is known to use a material which does not include high polarity elements such as nitrogen. Further, as disclosed in Japanese Unexamined Patent Publication No. 11-214382, in order to lower the density, it is known to introduce adamantane or another bulky structure having spaces in the molecule. Further, as disclosed in Japanese Unexamined Patent Publication No. 2001-332543, it is known to polymerize a compound having a three-dimensional structure and a compound having a two-dimensional structure so as to form molecular level pores. Further, as disclosed in Japanese Unexamined Patent Publication No. 2006-265513 above, it is known to use a pore forming agent to make a film porous. Further, as disclosed in Japanese Unexamined Patent Publication No. 2007-77289, it is known to use a composition including microparticles to form a film and thereby form a porous film.
However, a material obtained by using a pore forming agent to make a film porous exhibits a film permittivity of 2.2 or a lower value, but the mechanical strength is low and the pores are easily infiltrated by metals, various chemicals, etc. This is becoming a major problem in terms of reliability of semiconductor devices. Further, there are materials decreased in density without using a pore forming agent by introducing an adamantine-like structure and materials not including high polarity elements such as nitrogen where the permittivity is reduced to a value of over the 2.3 level, however, a permittivity 2.3 or less sought in the field of semiconductors has not been realized. In materials polymerizing two (or more) compounds and forming molecular level pores, explained above as another example, there are materials where the permittivity is 2.3 or less, but a reaction for polymerizing a plurality of compounds is based on an acid-base reaction or the like, so the material obtained by this is poor in storage stability. Further, depending on the reaction conditions (film-forming conditions), the degree of progress and uniformity of the reaction differ, so there was a problem that obtaining stable film properties was difficult. Further, forming a film from a composition including nanometer level particles to thereby form a porous low permittivity film is the same nano-structurally as using a pore forming agent to make a film porous. Further, the composition (coating solution) has particles dispersed in it, so the solid contents tend to precipitate due to the agglomeration of the particles and therefore the storage stability is inferior.